1. Field of the Invention
The present invention relates to drilling or boring apparatus for use in the drilling of holes in large sheet metal plates.
2. Prior Art
With the advent of the use of computer technology to control machinery in the mass production of essentially identical objects, it became possible to repeatively produce objects from sheet metal plates by controlling the movement of flame cutting assemblies over the plates. This type of apparatus is commonly referred to as numerically controlled flame cutting machines. Such apparatus are fairly sophisticated and capable of cutting intricate shapes from a sheet metal workpiece. The shapes may be varied by varying the program of the numerical control equipment and thus, such machines are highly versatile in the production of shapes of any desired external configuration.
However, it is still a problem to produce holes at desired locations within the objects so formed. The hole drilling or boring operation essentially becomes a manual step in which each object cut from the workpiece must be measured to lay out the proper hole locations and then aligned with a drilling or boring apparatus to produce the desired holes. This is a very expensive and time consuming means of locating and producing the holes since it requires repetitive passes on each object cut from the sheet metal plate.
Other means have been devised for accomplishing this aligning procedure on certain shapes of individual objects cut from the sheet metal workpieces, such as for example, the use of a fixture which clamps each object on a drilling table or jig which is then automatically moved relative to the drilling or boring apparatus to produce the holes at the desired locations. This is more accurate than manually locating each of the holes, however, it still requires the necessity of removing each individual piece from the flame cutting apparatus and properly positioning it on the drilling or boring apparatus. Thus, the manual labor involved is a considerable and expensive portion of this method of cutting holes.
Another difficulty associated with prior art methods and apparatus is that some of the objects which are cut by flame cutting apparatus from sheet metal workpieces are themselves relatively large and often require relatively large diameter holes, such as those over an inch in diameter, to be drilled at various locations on each of the objects. Conventional drilling and boring equipment for accomplishing the production of such large holes is extremely expensive and bulky and cannot be easily moved about the surface of the sheet metal plates in order to cut the holes prior to cutting of the objects from the plate. If it were possible to do this, however, it would be of substantial advantage since it would be possible to cut holes in a plurality of objects without the intervening step of removing the objects from the flame cutting apparatus and then aligning or positioning each object relative to the drilling or boring apparatus.
Flame cutting apparatus of the type to which the present invention is intended to be secured, generally comprise a pair of gantries supporting a cross bridge carrying the flame cutting assemblies which can be passed over the sheet metal plate to cut the plurality of objects from the plate. Because of this construction, the torque and drill feed pressure required on a drill to drill holes of diameters larger than approximately 1 inch would cause distortion in the bridge if the hole cutting apparatus was carried by the bridge. This would result in inaccurate location of the holes and unsatisfactory drilling. Thus, it has not been practical in the past to use such a hole cutting attachment on flame cutting apparatus of this type.
In addition, the burn tables upon which the sheet metal plates are supported are generally composed of either a plurality of bars which extend longitudinally or transversely of the sheet metal plate, or a plurality of points extending vertically upward and supporting the sheet metal plates. These points and bars tend to deflect standard twist drills as they penetrate through the back side of the plate, thus causing drill breakage, movement of the plate and/or distortions of the holes being drilled.